Water-borne resin composition and electrocoating composition

ABSTRACT

It is an object of the present invention to provide a water-borne resin composition which can form a film being excellent in flexibility and heat resistance without reducing an insulating property and can be used suitably for a cationic electrocoating composition. A water-borne resin composition, having a hydrolysable functional group and a polymerizable unsaturated carbon bond, wherein a base resin is at least one species selected from the group consisting of a polyamide-imide resin, a polyamide resin and a polyimide resin.

TECHNICAL FIELD

The present invention relates to a water-borne resin composition and anelectrocoating composition.

BACKGROUND ART

As undercoating of metal materials or the like, there is generallyemployed cationic electrodeposition having high corrosion resistance.Furthermore, as a special use, cationic electrodeposition may beutilized in order to form an electric insulating film on the metalmaterial. As a cationic electrocoating composition used in such thecationic electrodeposition, there is known a water-borne resincomposition, which contains an epoxy resin as a base resin and has ahydrolysable functional group and a polymerizable unsaturated carbonbond (cf. Japanese Kokai Publication 2000-038525). In order to obtain afilm having adequate heat resistance using such a resin, it is requiredto form a cured film having a high crosslinking density. Therefore,there were cases where the flexibility of the obtained film becameinsufficient and the processability of the film was reduced.

On the other hand, there is generally disclosed an electric insulatingcoating composition using a polyamide-imide resin, a polyamide resin anda polyimide resin as a base resin (cf. Japanese Kokai PublicationHei-05-295324 and Japanese Kokai Publication 2001-351441). It is knownthat these base resins can give a film having good heat resistance andexcellent flexibility even if a cured film having a high crosslinkingdensity is not necessarily formed because of high heat resistance of theresin itself. However, these electric insulating coating compositionscontain organic solvent in large amounts and have a problem from theviewpoint of environmental protection.

There are disclosed electrocoating compositions, which are water-bornecoatings and contain a polyimide resin, having such a function, as abase resin (cf. Japanese Kokai Publication Hei-09-124978 and JapaneseKokai Publication 2002-38078). However, since such the electrocoatingcompositions had insufficient stability, they were not substancescapable of with standing long-term uses. And the obtained film did nothave a sufficient film thickness and a satisfactory electricalinsulating property.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a water-borne resincomposition which can form a film being excellent in flexibility andheat resistance without reducing an insulating property and can be usedsuitably for a cationic electrocoating composition.

The present invention relates to a water-borne resin composition, havinga hydrolysable functional group and a polymerizable unsaturated carbonbond,

-   -   wherein a base resin is at least one species selected from the        group consisting of a polyamide-imide resin, a polyamide resin        and a polyimide resin.

The above-mentioned hydrolysable functional group is preferably an oniumgroup.

The above-mentioned onium group is preferably a sulfonium group.

The above-mentioned polymerizable unsaturated carbon bond preferablyderives from a propargyl group.

Preferably, the above-mentioned water-borne resin composition contains asulfonium group in an amount of 5 to 100 mmol and a propargyl group inan amount of 10 to 150 mmol per 100 g of the resin solids and the totalcontent of the sulfonium group and the propargyl group is 200 mmol orless per 100 g of the resin solids.

The present invention also relates to an electrocoating compositioncomprising the above water-borne resin composition.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail.

A water-borne resin composition of the present invention is a substance,which has a hydrolysable functional group and a polymerizableunsaturated carbon bond and contains at least one species selected fromthe group consisting of a polyamide-imide resin, a polyamide resin and apolyimide resin as a base resin. By containing the above-mentioned atleast one species selected from the group consisting of thepolyamide-imide resin, the polyamide resin and the polyimide resin as abase resin, the water-borne resin composition of the present inventioncan attain a film which is excellent in an electrical insulatingproperty, heat resistance, processability and flexibility. And, since itcan be treated in an aqueous condition, it is safe and can reduce avolatile organic compound (VOC).

The above-mentioned water-borne resin composition is one which can beused suitably for electrodeposition. Since it can be applied byelectrodeposition, it can be uniformly applied to a substrate and canform a coat, which has less variations in a film thickness, on thesubstrate even for a substrate having a complex configuration.

A base resin of the water-borne resin composition of the presentinvention is at least one species selected from the group consisting ofa polyamide-imide resin, a polyamide resin and a polyimide resin. Sincethe water-borne resin composition of the present invention containsthese resins as a base resin, it can exert good heat resistance. Theabove-mentioned polyamide resin is not particularly limited and forexample, a compound, prepared by blending a dicarboxylic acid with adiamine compound or diisocyanate and polycondensing them, or a compound,prepared by blending a halogenated dicarboxylic acid with a diaminecompound and conducting de-hydrogen halide reaction, can be given. Theabove-mentioned polyimide resin is not particularly limited and forexample, a compound, prepared by blending tetracarboxylic dianhydridewith a diamine compound or diisocyanate and polycondensing them, can begiven. The above-mentioned polyamide-imide resin is not particularlylimited and for example, a compound, prepared by blending tricarboxylicanhydride with a diamine compound or diisocyanate and polycondensingthem, can be given.

As the above-mentioned dicarboxylic acid, there can be given,specifically, aliphatic dicarboxylic acids or derivatives thereof suchas adipic acid, azelaic acid and sebacic acid; and aromatic or alicyclicdicarboxylic acids or derivatives thereof such as terephthalic acid,isophthalic acid, 2-chloroterephthalic acid, terephthalic aciddichloride, 2-methyl terephthalate, 5-methyl isoterephthalate,hexahydroterephthalic acid, and hexahydroisophthalic acid.

As the above-mentioned tetracarboxylic dianhydride, there can be given,specifically, pyromellitic dianhydride,3,4,3′,4′-benzophenonetetracarboxylic dianhydride,3,4,3′,4′-diphenylsulfontetracarboxylic dianhydride,bis-(3,4-dicarboxyphenyl) ether anhydride,2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, and thelike.

As the above-mentioned tricarboxylic anhydride, there can be given,specifically, tricarboxylic anhydrides and derivatives thereof such asbutanetricarboxylic anhydride, trimellitic anhydride,benzophenonetricarboxylic anhydride, diphenylsulfontricarboxylicanhydride, diphenyl ether tricarboxylic anhydride, diphenyltricarboxylic anhydride, diphenylpropanetricarboxylic anhydride anddiphenylhexafluoropropanetricarboxylic anhydride.

As the above-mentioned diamine compound, there can be given,specifically, aliphatic diamine compounds such as hexamethylene diamine,tetramethylene diamine and 4,4′-diaminocyclohexane; and aromatic diaminecompounds such as p-phenylenediamine, m-phenylenediamine,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether and2,4-dimethyl-m-phenylenediamine.

As the above-mentioned diisocyanate, there can be given, specifically,aliphatic diisocyanates such as hexamethylene diisocyanate (HMDI),isophorone diisocyanate (IPDI), 4,4′-methylenebis(cyclohexyl isocyanate)(hydrogenated MDI) and norbornene diisocyanate (NBDI); and aromaticdiisocyanates such as trilene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI) and xylylene diisocyanate (XDI). And, alcohol-blockedtypes thereof can be used.

Among others, the base resin of the water-borne resin composition of thepresent invention is preferably a polyamide-imide resin in point of theheat resistance and the ease of synthesis.

The above-mentioned water-borne resin composition has a hydrolysablefunctional group and a polymerizable unsaturated carbon bond. Theabove-mentioned base resin constituting the water-borne resincomposition may contain both a hydrolysable functional group and apolymerizable unsaturated carbon bond in a molecule, but it does notnecessarily do so. Thus, for example, the base resin may have onlyeither the hydrolysable functional group or the polymerizableunsaturated carbon bond in a molecule. In the latter case, the wholeresin composition has both of these two species. That is, the abovewater-borne resin composition may comprise a resin having thehydrolysable functional group and the polymerizable unsaturated carbonbond, a mixture of a resin having only the hydrolysable functional groupand a resin having only the polymerizable unsaturated carbon bond, or amixture of all of these resins. It is herein defined in the above sensethat the above water-borne resin composition has the hydrolysablefunctional group and the polymerizable unsaturated carbon bond.

The above-mentioned hydrolysable functional group is not particularlylimited and for example, onium groups such as an ammonium group, asulfonium group and a phosphonium group can be given. Among others, anammonium group and a sulfonium group are preferred because of highadhesion to metal substrates, and among others, a sulfonium group ismore preferred.

Further, the water-borne resin composition of the present invention hasa polymerizable unsaturated carbon bond. That is, a film is formed by acuring reaction through the polymerization of the polymerizableunsaturated carbon bond. Since curing of the coat proceeds by such acuring reaction, an amount of production of volatile components can bereduced in curing and therefore it is possible to prevent an electricinsulating property from deteriorating due to voids in a coat resultingfrom volatile components in a coat.

The above-mentioned polymerizable unsaturated carbon bond is notparticularly limited as long as it forms a curing system in whichpolymerization of the unsaturated bond allows a reaction to proceed. Assuch a carbon bond, there may be given polymerizable unsaturated carbonbonds, forming curing systems such as a propargyl-allene curing system,a curing system based on Michael addition reaction of an activemethylene group to an α, β-unsaturated bond and a curing system based onoxidative polymerization. Among others, this bond is preferably apolymerizable unsaturated carbon bond forming the propargyl-allenecuring system because the combined use of this bond and the above oniumgroup accelerates a curing reaction. That is, the water-borne resincomposition of the present invention preferably contains a propargylgroup.

Preferably, the water-borne resin composition of the present inventioncontains a sulfonium group and a propargyl group. When the water-borneresin composition containing the above-mentioned sulfonium group andpropargyl group is used as a cationic electrocoating composition, as anelectric voltage or current above a certain level is provided in theelectrodeposition step, the sulfonium group is subjected to anelectrolytic reduction reaction on the electrode, and thereby the ionicgroup thereof disappears and the sulfonium group can be irreversiblypassivated and precipitated. It is considered that, in thiselectrodeposition step, the electrode reaction provoked generates thehydroxide ion, which is held by the sulfonium ion, with the result thatan electrolytically generated base is formed in the coat. Thiselectrolytically generated base can convert the propargyl group existingin the coat and being low in reactivity upon heating to the allene bondhigh in reactivity upon heating. That is, polymerization derived fromthe allene bond proceeds in heat curing after the electrodeposition stepand a curing reaction is accelerated. Thus, it is possible to attain afilm having high adhesion to a substrate by containing these twofunctional groups.

When the above-mentioned water-borne resin composition has the sulfoniumgroup and the propargyl group, it is preferred that the content of thesulfonium group in the above water-borne resin composition lies within arange of 5 mmol (lower limit) to 100 mmol (upper limit) per 100 g of theresin solids. When this content is less than 5 mmol per 100 g of theresin solids, curability cannot be adequately exerted, andhydrolysability and bath stability deteriorate. When it is more than 100mmol per 100 g of the resin solids, the coat deposition on the surfaceof a substrate becomes poor. In addition, as for the content of theabove-mentioned sulfonium group, amore preferable content can beselected in accordance with the resin skeleton employed.

When the above-mentioned water-borne resin composition has the sulfoniumgroup and the propargyl group, it is preferred that the content of thepropargyl group, which the above water-borne resin composition has, isin a range of 10 mmol (lower limit) to 150 mmol (upper limit) per 100 gof the resin solids. When the above content is less than 10 mmol per 100g of the resin solids, curability cannot be adequately exerted, and whenit is more than 150 mmol per 100 g of the resin solids, the flexibilityof the obtained film may deteriorate. In addition, as for the content ofthe above-mentioned propargyl group, a more preferable content can beselected in accordance with the resin skeleton employed.

When the above-mentioned water-borne resin composition has the sulfoniumgroup and the propargyl group, it is preferred that the total content ofthe sulfonium group and the propargyl group, which the above water-borneresin composition has, is preferably 200 mmol or less per 100 g of theresin solids. When this content is more than 200 mmol per 100 g of theresin solids, a resin may not be obtained in fact or an intendedperformance may not be attained. In addition, as for the above totalcontent of the sulfonium group and the propargyl group, a morepreferable content can be selected in accordance with the resin skeletonemployed.

Part of the propargyl group in the above water-borne resin compositionmay be converted to an acetylide. An acetylide is a salt-like acetylatedmetal compound. As for the content of the propargyl group to beconverted to an acetylide in the above water-borne resin composition,preferably, the lower limit is 0.1 mmol and the upper limit is 40 mmolper 100 g of the resin solids. When this content is less than 0.1 mmolper 100 g of the resin solids, the effect of the conversion to anacetylide is not sufficiently exerted, and when it is more than 40 mmolper 100 g of the resin solids, the conversion to an acetylide isdifficult. As for this content, a more preferable range can be selectedin accordance with the metal species employed.

A metal contained in the above-mentioned propargyl group converted to anacetylide is not particularly limited as long as it presents a catalyticaction and includes, for example, transition metals such as copper,silver, barium, and the like. If the conformity with an environment isconsidered, copper and silver are preferred among these and copper ismore preferable from the viewpoint of the ready availability. Whencopper is used as the above-mentioned metal, the content of thepropargyl group to be converted to an acetylide in the above water-borneresin composition is more preferably 0.1 to 20 mmol per 100 g of theresin solids.

By converting part of the propargyl group in the above water-borne resincomposition to an acetylide, a curing catalyst can be introduced intothe resin composition. When the resin composition is prepared in thismanner, it is generally unnecessary to use an organic transition metalcomplex which is difficult to dissolve or disperse in organic solventsand water and is possible to introduce even a transition metal easilythrough conversion to an acetylide, and therefore even ahard-to-dissolve transition metal compound is applicable to a coatingcomposition without restraint. Further, the occurrence of an organicacid salt as an anion in the electrodeposition bath, which isencountered when a transition metal organic acid salt is used, can beavoided and furthermore, the metal ion will not be removed through ultrafiltration, hence the bath management and the design of coatingcompositions become easy.

A weight-average molecular weight of the water-borne resin compositionof the present invention is preferably within a range of 1000 (lowerlimit) to 5000 (upper limit). When the weight-average molecular weightis less than 1000, the heat resistance and the flexibility deteriorate,and when it is more than 5000, a good coat cannot be formed on thesurface of a metal substrate. As for the above weight-average molecularweight, a more preferable molecular weight can be selected in accordancewith the resin skeleton.

The above water-borne resin composition may contain a carbon-carbondouble bond where desired. Since the above-mentioned carbon-carbondouble bond has high reactivity, curability can be further enhanced.

A method of introducing the above sulfonium group and propargyl group isnot particularly limited. As such a method, there can be given, forexample, a method (I) comprising the step (i) of reacting an epoxycompound with a compound having a functional group reacting with anepoxy group and a propargyl group to obtain an epoxy compound containinga propargyl group and the step (ii) of reacting a polyamide resin, apolyimide resin or a polyamide-imide resin, and the epoxy compoundcontaining a propargyl group obtained in the step (i), and asulfide/acid mixture to introduce the propargyl group and the sulfoniumgroup.

As the above-mentioned compound having a functional group reacting withthe epoxy group and a propargyl group (hereinafter, referred to as“compound (A)”), there may be used, for example, a compound having botha functional group reacting with the epoxy group, such as a hydroxyl orcarboxyl group, and a propargyl group, and specifically, there may begiven propargyl alcohol and propargylic acid. Among these, propargylalcohol is preferred from the viewpoint of its ready availability andease of reaction.

In providing the above resin composition with a carbon-carbon doublebond as required, a compound containing a functional group reacting withthe epoxy group and a carbon-carbon double bond (hereinafter, referredto as “compound (B)”) may be used in combination with theabove-mentioned compound (A) in the above-mentioned step (i). As theabove-mentioned compound (B), there may be used a compound containingboth a functional group reacting with the epoxy group, such as ahydroxyl or carboxyl group, and a carbon-carbon double bond.

In the above step (i), the epoxy compound is reacted with the abovecompound (A) to obtain an epoxy compound containing the propargyl group,or the epoxy compound is reacted with the above compound (A) and, asrequired, the above compound (B) to obtain an epoxy compound containingthe propargyl group and the carbon-carbon double bond. In this lattercase, in the step (i), the compound (A) and the compound (B) may bemixed together in advance and then subjected to a reaction, or thecompound (A) and the compound (B) may be separately subjected to areaction. In addition, the above functional group reacting with theepoxy group, which the compound (A) has, and the functional groupreacting with the epoxy group, which the compound (B) has, may be thesame or different.

As for the conditions of a reaction in the above step (i), the reactionis generally carried out at room temperature or at a temperature of 80to 140° C. for several hours. And, publicly known ingredients, which arerequired for the progress of the reaction, such as a catalyst and/or asolvent may be used as required. The completion of the reaction can bechecked by measuring an epoxy equivalent, and the functional groupintroduced can be identified by analysis of non-volatile content or byinstrumental analysis of the resin composition obtained. The reactionproduct thus obtained is generally a mixture of epoxy compounds havingone or more propargyl groups, or a mixture of epoxy compounds having oneor more propargyl groups and carbon-carbon double bonds. In this sense,through the above step (i), there is obtained the epoxy compoundcontaining a propargyl group.

In the step (ii), by reacting a polyamide-imide resin, a polyamide resinor a polyimide resin, and the epoxy compound containing a propargylgroup obtained in the step (i), and the sulfide/acid mixture, thesulfonium group is introduced in the epoxy group, and further theresulting epoxy compound having the propargyl group and the sulfoniumgroup is reacted with a polyamide-imide resin, a polyamide resin or apolyimide resin. The introduction of the sulfonium group can beperformed by a method of reacting the epoxy group with the sulfide/acidmixture to conduct the introduction of the sulfide and the conversion ofthe sulfide to the sulfonium group, or a method in which a sulfide isintroduced and then the introduced sulfide is converted to a sulfoniumgroup by a reaction with an acid or an alkyl halide such as methylfluoride, methyl chloride or methyl bromide, or the like, if necessary,followed by anion exchange. From the viewpoint of the ready availabilityof reaction materials, the method using a sulfide/acid mixture ispreferred.

The above-mentioned sulfide is not particularly limited, and forexample, aliphatic sulfides, aliphatic-aromatic mixed sulfides, aralkylsulfides, and cyclic sulfides can be given. Specifically, there can begiven, for example, diethyl sulfide, dipropyl sulfide, dibutyl sulfide,dihexyl sulfide, diphenyl sulfide, ethyl phenyl sulfide, tetramethylenesulfide, pentamethylene sulfide, thiodiethanol, thiodipropanol,thiodibutanol, 1-(2-hydroxyethylthio)-2-propanol,1-(2-hydroxyethylthio)-2-butanol, and1-(2-hydroxyethylthio)-3-butoxy-1-propanol.

The above-mentioned acid is not particularly limited, and for example,formic acid, acetic acid, lactic acid, propionic acid, boric acid,butyric acid, dimethylolpropionic acid, hydrochloric acid, sulfuricacid, phosphoric acid, N-acetylglycine, and N-acetyl-β-alanine can begiven.

Preferably, the mixing ratio between the above sulfide and the aboveacid in the above sulfide/acid mixture is generally about 100/40 to100/100 as expressed in terms of sulfide/acid mole ratio.

The reaction in the above step (ii) can be carried out, for example, bymixing a mixture of the epoxy compound containing a propargyl group,obtained in the above step (i), and the predetermined amount of theabove sulfide/acid mixture, which have been set, for instance, so as togive the above-mentioned sulfonium group content, with water being 5 to10 times in mole more than the sulfide used and stirring the mixturegenerally at 50 to 90° C. for several hours. A residual acid value of 5or smaller may serve as a criterion in judging the reaction to becompleted. The introduction of the sulfonium group in the water-borneresin composition obtained can be identified by potentiometrictitration.

The same procedure can be used also in the case where the sulfide isintroduced and then the introduced sulfide is converted to the sulfoniumgroup. By introducing the sulfonium group after introduction of thepropargyl group, as described above, the sulfonium group can beprevented from being decomposed due to heating.

As a method of introducing the above sulfonium group and propargylgroup, in addition to the above method (I), there can be given a method(II) in which a compound formed by adding an epoxy group and/or apropargyl group to a monomer as a raw material is used and polymerizedin producing a polyamide resin, a polyimide resin or a polyamide-imideresin, which is a base resin, and then the obtained resin is reactedwith a sulfide/acid mixture to introduce the sulfonium group. And, inthe case where the base resin is a polyamide resin, there can be given amethod (III) in which after a polyamide resin is produced, the polyamideresin is reacted with a compound having a functional group reacting witha functional group of a terminal of the polyamide and a propargyl group,and then reacted with a sulfide/acid mixture to introduce the propargylgroup and the sulfonium group.

The above-mentioned monomer, to which an epoxy group and/or a propargylgroup is added, is not particularly limited and for example, a compoundformed by adding propargyl alcohol to pyromellitic anhydride ortrimellitic anhydride can be used.

And, the above-mentioned compound, having a functional group reactingwith a functional group of a terminal of the polyamide and a propargylgroup, is not particularly limited and for example, a compound, formedby adding propargylic acid to a polyfunctional epoxy compound such astrimethylolpropane triglycidyl ether or the like, can be used.

When part of the propargyl group in the above resin composition isconverted to an acetylide, in the case of utilizing the method (I), theconversion to the acetylide can be carried out by the step of reactingthe epoxy compound containing a propargyl group, obtained in the abovestep (i) with a metal compound to thereby convert part of the propargylgroup in the above epoxy compound to the corresponding acetylide. Theabove-mentioned metal compound is preferably a transition metal compoundcapable of giving an acetylide and for example, complexes or salts oftransition metals described above can be given. Specifically, there canbe given, for example, acetylacetone copper, copper acetate,acetylacetone silver, silver acetate, silver nitrate, acetyl acetonebarium, and barium acetate. Among these, copper or silver compounds arepreferred from the viewpoint of the conformity with an environment, andcopper compounds are more preferred because of their ready availability.For example, acetylacetone copper is suitably used in view of the easeof bath control.

Further, in the case of utilizing the method (I), the step of convertingpart of the propargyl group in the epoxy compound to an acetylide andthe above step (ii) can be carried out under common reaction conditions,so that both steps can be carried out simultaneously. The method ofcarrying out both steps simultaneously can advantageously simplify theproduction process.

In this way, the resin composition containing a propargyl group and asulfonium group, and optionally containing a carbon-carbon double bondand/or a propargyl group-derived acetylide as required can be producedwhile preventing the sulfonium group from being decomposed.Incidentally, acetylides in a dry state are explosive but the reactionin the practice of the invention is carried out in a water-borne mediumand the intended substance can be obtained in the form of a water-bornecomposition. Therefore, there arises no safety problem.

The water-borne resin composition of the present invention is formed bydispersing the resin composition obtained in a manner described above ina water-borne medium. The above-mentioned water-borne medium is notparticularly limited and for example, water and a mixed solvent of waterand another solvent can be given. The above-mentioned another solvent isnot particularly limited as long as it exhibits compatibility with waterand for example, hydrocarbons (for example, xylene or toluene), alcohols(for example, methyl alcohol, n-butyl alcohol, isopropyl alcohol,2-ethylhexyl alcohol, ethylene glycol, propylene glycol), ethers (forexample, ethylene glycol monoethyl ether, ethylene glycol monobutylether, ethylene glycol monohexyl ether, propylene glycol monoethylether, 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether), ketones (for example, methylisobutyl ketone, cyclohexanone, isophorone, acetyl acetone), esters (forexample, ethylene glycol monoethyl ether acetate, ethylene glycolmonobutyl ether acetate), and mixtures thereof can be given.

The present invention is also an electrocoating composition comprisingthe above-mentioned water-borne resin composition. Since theabove-mentioned electrocoating composition contains the water-borneresin composition described above and is applied by electrodeposition,it can provide a film, which is uniform and excellent in heatresistance, processability and flexibility, for an article to be coatedhaving a complex configuration.

The above-mentioned electrocoating composition does not necessarily needto use a curing agent since the resin composition itself contained inthe electrocoating composition has the curability. But, the curing agentmay be used to further enhance the curability. As such a curing agent,there can be given, for example, a compound obtained by adding acompound having a propargyl group such as propargyl alcohol and the likeand a compound having a carbon-carbon double bond such as acrylic acidand the like to a compound containing a plurality of at least onespecies of a propargyl group and a carbon-carbon double bond, e.g.polyepoxide such as novolac phenol and pentaerythrite tetraglycidylether.

It is not always necessary to use a curing catalyst in the aboveelectrocoating composition. However, when a further improvement incurability is required depending on the curing reaction conditions, atransition metal compound generally to be used may be appropriatelyadded as required. Such a compound is not particularly limited butincludes, among others, complexes or compounds formed by combining aligand, such as cyclopentadiene or acetylacetone, or a carboxylic acidsuch as acetic acid, with transition metals such as nickel, cobalt,manganese, palladium, and rhodium. The amount of the above curingcatalyst to be added is preferably in a range of 0.1 mmol (lower limit)to 20 mmol (upper limit) per 100 g of the resin solids in theelectrocoating composition.

An amine may further be blended in the electrocoating composition of thepresent invention. By the addition of the above amine, the conversionrate of the sulfonium group to a sulfide by electrolytic reduction inthe process of electrodeposition is increased. The above-mentioned amineis not particularly limited and for example, amine compounds such asprimary to tertiary monofunctional or polyfunctional aliphatic amines,alicyclic amines and aromatic amines can be given. Among these,water-soluble or water-dispersible ones are preferred. As such theamines, there may be given, for example, alkylamines having 2 to 8carbon atoms such as monomethylamine, dimethylamine, trimethylamine,triethylamine, propylamine, diisopropylamine and tributylamine;monoethanolamine, dimethanolamine, methylethanolamine,dimethylethanolamine, cyclohexylamine, morpholine, N-methylmorpholine,pyridine, pyrazine, piperidine, imidazoline, imidazole and the like.These may be used alone or two or more of them may be used incombination. Among others, hydroxy amines such as monoethanolamine,diethanolamine and dimethylethanolamine are preferred because of theexcellent dispersion stability in water.

The above amine can be directly blended in the electrocoatingcomposition of the present invention. While in the conventionalneutralized amine type cationic electrocoating, the addition of a freeamine results in deprivation of the neutralizing acid in the resin,hence in marked deterioration of the stability of the electrodepositionsolution, no such bath stability trouble will arise in the presentinvention.

The amount of the above amine to be blended is preferably in a range of0.3 to 100 milliequivalents (meq) per 100 g of the resin solids in theelectrocoating composition. When this amount is less than 0.3 meq/100 g,an adequate effect on a throwing power cannot be attained. When itexceeds 100 meq/100 g, the effects proportional to the addition amountcannot be obtained and this is not economical. This amount is morepreferably in a range of 1 to 15 meq/100 g.

In the electrocoating composition of the present invention, there mayalso be blended an aliphatic hydrocarbon group-containing resincomposition. By blending the above-mentioned aliphatic hydrocarbongroup-containing resin composition, the shock resistance of the film tobe obtained is improved. As the aliphatic hydrocarbon group-containingresin composition, there may be mentioned those containing, per 100 g ofthe resin solids, 5 to 400 mmol of a sulfonium group, 80 to 135 mmol ofan aliphatic hydrocarbon group containing 8 to 24 carbon atoms andoptionally containing an unsaturated double bond in the chain thereofand 10 to 315 mmol of at least one of a propargyl group and organicgroups containing 3 to 7 carbon atoms and having a terminal unsaturateddouble bond on condition that the total content of the sulfonium group,the aliphatic hydrocarbon group containing 8 to 24 carbon atoms andoptionally containing an unsaturated double bond in the chain thereofand the propargyl group and organic groups containing 3 to 7 carbonatoms and having a terminal unsaturated double bond is not more than 500mmol per 100 g of the resin solids.

When such an aliphatic hydrocarbon group-containing resin composition isblended in the above electrocoating composition, the resin solids in theelectrocoating composition preferably contains, per 100 g thereof, 5 to400 mmol of sulfonium group, 10 to 300 mmol of the aliphatic hydrocarbongroup containing 8 to 24 carbon atoms and optionally containing anunsaturated double bond in the chain thereof and a total of 10 to 485mmol of the propargyl group and organic groups containing 3 to 7 carbonatoms and having a terminal unsaturated double bond, and the totalcontent of the sulfonium group, the aliphatic hydrocarbon groupcontaining 8 to 24 carbon atoms and optionally containing an unsaturateddouble bond in the chain thereof, the propargyl group and the organicgroups containing 3 to 7 carbon atoms and having a terminal unsaturateddouble bond is not more than 500 mmol per 100 g of the resin solids inthe electrocoating composition, and the content of the aliphatichydrocarbon group containing 8 to 24 carbon atoms and optionallycontaining an unsaturated double bond in the chain thereof is 3 to 30%by weight relative to the resin solids in the electrocoatingcomposition.

When the aliphatic hydrocarbon group-containing resin composition isblended in the above electrocoating composition and the sulfonium groupcontent level is lower than 5 mmol/100 g, any satisfactory throwingpower or curability cannot be attained and, further, the hydrolysabilityand bath stability will be poor. When it exceeds 400 mmol/100 g, thedeposition of coatings on the surface of the articles to be coatedworsens. When the content of the aliphatic hydrocarbon group containing8 to 24 carbon atoms and optionally containing an unsaturated doublebond in the chain thereof is less than 80 mmol/100 g, the shockresistance will not be improved to a satisfactory extent and, when itexceeds 350 mmol/100 g, the resin composition becomes difficult tohandle. When the total content of the propargyl group and the organicgroups containing 3 to 7 carbon atoms and having a terminal unsaturateddouble bond is less than 10 mmol/100 g, no satisfactory curability canbe manifested on the occasion of combined use of another resin and/oranother curing agent and, when it exceeds 315 mmol/100 g, the shockresistance will not be improved to a satisfactory extent. The totalcontent of the sulfonium group, the aliphatic hydrocarbon groupcontaining 8 to 24 carbon atoms and optionally having an unsaturateddouble bond in the chain thereof, the propargyl group and the organicgroups containing 3 to 7 carbon atoms and having a terminal unsaturateddouble bond is not more than 500 mmol per 100 g of the resin solids.When it exceeds 500 mmol, any corresponding resin cannot be obtained inactuality or the desired performance characteristics cannot be obtainedin some instances.

The above electrocoating composition may further contain othercomponents used in an ordinary electrocoating as required. Theabove-mentioned another component is not particularly limited, and forexample, a pigment, a rust preventive, a pigment dispersion resin, asurfactant, an antioxidant and an ultraviolet absorber can be given.

The above-mentioned pigment is not particularly limited, and forexample, coloring pigments such as titanium dioxide, carbon black, rediron oxide, and the like; rust-preventive pigments such as basic leadsilicate, aluminum phosphomolybdate, and the like: and extender pigmentssuch as kaoline, clay, talc, and the like, can be given. As theabove-mentioned rust preventive, specifically, there may be givencalcium phosphite, zinc calcium phosphite, calcium-carrying silica,calcium-carrying zeolite, and the like. The total amount of the abovepigments and rust preventives to be blended is preferably in a range of0 weight % (lower limit) to 50 weight % (upper limit) in terms of thesolid content in the above electrocoating composition.

The above pigment dispersion resins are used to stably disperse theabove pigments in the electrocoating composition. The pigment dispersionresins are not particularly restricted and pigment dispersion resinswhich are in general use can be employed.

When electrodeposition is performed using the electrocoating compositionof the present invention, the article to be coated is not particularlylimited as long as it is one exhibitting conductivity, and for example,an iron sheet, a steel sheet, an aluminum sheet, and articles formed bysurface treating or molding these can be given.

As electrodeposition, there may be given, for example, cationicelectrodeposition conducted by utilizing an article to be coated as acathode and applying a voltage generally within the range of 50 to 450 Vbetween the cathode and an anode. When the voltage applied is lower than50 V, electrodeposition becomes insufficient. When the voltage exceeds450 V, the power consumption uneconomically increases. When theelectrocoating composition of the present invention is used and avoltage within the above range is applied, a uniform coat can be formedon the whole article to be coated without any rapid increase in filmthickness in the process of electrodeposition. In ordinary cases, a bathtemperature of the electrocoating composition in applying the abovevoltage is preferably 10 to 60° C.

An electrodeposition process preferably comprises (1) a process ofimmersing an article to be coated in an electrocoating composition and(2) a process of utilizing the above article to be coated as a cathodeand applying a voltage between the cathode and an anode to deposit acoat. Though a duration during which a voltage is applied variesdepending on the conditions of electrodeposition, it may be generallyset at a duration of 2 to 4 minutes.

An electrodeposited coat obtained in a manner described above can becure by being baked at a temperature of 150 to 260° C. for 10 to 30minutes as is or following washing with water after the completion ofthe electrodeposition process to obtain a cured film.

A film thickness of the above cured electrodeposited film is preferablywithin a range of 5 μm (lower limit) to 200 μm (upper limit). When thefilm thickness is out of the above range, a film to be obtained maybecome uneven.

The article to be coated, on which a film thus obtained is formed, maybe further coated with an intermediate coating composition and/or a topcoating composition in accordance with a purpose.

The water-borne resin composition of the present invention contains atleast one species selected from the group consisting of apolyamide-imide resin, a polyamide resin and a polyimide resin, whichare excellent in the heat resistance and the flexibility, as a baseresin and can be suitably applied by electrodeposition which isexcellent in the workability of coating. And, the above water-borneresin composition can attain a film having high adhesion because it hasa hydrolysable functional group and a polymerizable unsaturated carbonbond. Further, since the base resin of the above resin composition is atleast one species selected from the group consisting of apolyamide-imide resin, a polyamide resin and a polyimide resin, the filmto be obtained from the above resin composition also has a highinsulating property.

It is possible to produce the film being excellent in the heatresistance and the flexibility by using the water-borne resincomposition of the present invention. Thereby, the processability of thefilm is also improved and the film becomes applicable to the electricand electronic fields. Also, since the water-borne resin composition ofthe present invention is used suitably for the electrodeposition, it ispossible to apply a coating efficiently even to an article to be coatedhaving a complex configuration.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail byway of examples, but the present invention is not limited to theseexamples. In addition, “part(s)” refers to “part(s) by weight” inExamples, unless otherwise specified.

EXAMPLE 1

In a separable flask equipped with a stirrer, a thermometer, a nitrogengas inlet tube and a reflux cooling tube, 431 parts by weight ofEPOTOHTO YH-300 with an epoxy equivalent of 144 (an epoxy compoundproduced by Tohto Kasei Co., Ltd.) and 180 parts by weight of propargylalcohol were put, and the mixture was heated to 125° C. and reacted atthat temperature for 5 hours to obtain an epoxy compound containing apropargyl group.

321 parts by weight of N-methyl-2-pyrrolidone, 192 parts by weight oftrimellitic anhydride, and 200 parts by weight ofdiphenylmethane-4,4′-diisocyanate were put in a separable flask equippedwith a stirrer, a thermometer, a nitrogen gas inlet tube and a refluxcooling tube, and the mixture was heated to 150° C. and reacted at thattemperature for 10 hours to obtain a resin composition.

This product was cooled to 80° C. and to this was added 243 parts byweight of the epoxy compound containing a propargyl group previouslyprepared, and this mixture was reacted for 5 hours. To this were added54 parts by weight of 1-(2-hydroxyethylthio)propane-2-ol, 19 parts byweight of glacial acetic acid and 57 parts by weight of deionized water,and the mixture was reacted for 6 hours while maintaining thetemperature at 75° C. After verifying that an acid value is 5 or less,2273 parts by weight of deionized water was added to give an intendedwater-borne resin composition. This resin composition had a resin solidscontent of 20 weight % and the sulfonium group was 28 mmol/100 gvarnish.

COMPARATIVE EXAMPLE 1

In a separable flask equipped with a stirrer, a thermometer, a nitrogengas inlet tube and a reflux cooling tube, 234 parts by weight ofEPOTOHTO YDCN-703 with an epoxy equivalent of 203 (an epoxy compoundproduced by Tohto Kasei Co., Ltd.) and 101 parts by weight of propargylalcohol were put, and the mixture was heated to 125° C. and reacted atthat temperature for 5 hours to obtain an epoxy compound containing apropargyl group.

This product was cooled to 80° C. and to this were added 27 parts byweight of 1-(2-hydroxyethylthio)propane-2-ol, 29 parts by weight ofglacial acetic acid and 10 parts by weight of deionized water, and themixture was reacted for 6 hours while maintaining the temperature at 75°C. After verifying that an acid value is 5 or less, 1222 parts by weightof deionized water was added to give an intended water-borne resincomposition. This resin composition had a resin solids content of 20weight % and the sulfonium group was 28 mmol/100 g varnish.

Evaluation Test

The water-borne resin compositions prepared in Example 1 and ComparativeExample 1 were put in a 4 liter, stainless steel container and thus, anelectrodeposition bath was constituted. A copper plate having athickness of 0.3 mm and a size of 35 mm×75 mm was placed in anelectrodeposition bath liquid and electrodeposition coated so as to be100 μm in a dried film thickness. After the resulting copper plates werewashed with water, they were cured by heating at 250° C. for 20 minutesto obtain electrodeposition films. The following evaluations wereperformed on the obtained electrodeposition films and the results wereshown in Table 1.

-(1) Flexibility Test

The presence or absence of cracks of each film was investigated by usinga steel rod of 5 mm in diameter as a bending central line and bendingthe coated copper plate around the steel rod by an angle of 180° at 25°C. for 0.5 seconds.

(2) Heat Resistance Test

Each film on the copper plate was heated at 250° C. for 24 hours and aratio of remaining weight was determined from weights measured beforeand after heating.

(3) Insulating Property Test

The measuring terminals of a withstand voltage tester Model 8525(manufactured by Tsuruga Electric Corporation) were connected to aconductive portion of the copper plate and a portion of the obtainedelectrodeposition film and a dielectric breakdown voltage was measuredunder the condition of 500 V/s. TABLE 1 Comparative Example 1 Example 1Flexibility No cracks Cracks were found. Heat resistance (weight %) 9690 Insulating property (kV) 9.7 9.6

It was shown from Table 1 that the film, which was obtained by using thewater-borne resin composition of the present invention, was excellent inthe flexibility, the heat resistance and the insulating property.

1. A water-borne resin composition, having a hydrolysable functionalgroup and a polymerizable unsaturated carbon bond, wherein a base resinis at least one species selected from the group consisting of apolyamide-imide resin, a polyamide resin and a polyimide resin.
 2. Thewater-borne resin composition according to claim 1, wherein thehydrolysable functional group is an onium group.
 3. The water-borneresin composition according to claim 2, wherein the onium group is asulfonium group.
 4. The water-borne resin composition according to anyone of claims 1 to 3, wherein the polymerizable unsaturated carbon bondderives from a propargyl group.
 5. The water-borne resin compositionaccording to claim 4, wherein said water-borne resin compositioncontains a sulfonium group in an amount of 5 to 100 mmol and a propargylgroup in an amount of 10 to 150 mmol per 100 g of the resin solids andthe total content of said sulfonium group and said propargyl group is200 mmol or less per 100 g of the resin solids.
 6. An electrocoatingcomposition, comprising the water-borne resin composition according toany one of claims 1 to 3.